The present invention is directed to a double band press or a single or multiplaten press, with heatable or coolable parts, and to the process for the fabrication of these parts.
Double band presses are used for continuous pressing or extrusion of material webs. These presses exert a uniform area pressure upon the material to be pressed or molded by means of endless press bands arranged one above the other and conducted over reversing drums, while, at the same time, the commodity to be pressed is continuously conveyed through the double band press (see DE-OS 24 21 296). Such material webs can, for instance, consist of several layers of paper webs, woven glass fiber webs, laminated webs with metal foil placed thereon, fiber binder mixtures of the like, which are stacked one upon the other and impregnated with duroplastic or thermoplastic resins. These materials webs can require the use of a specific temperature during the extrusion process, in order to cure the binder contained in the material web and to connect the individual layers with each other to form a compact, pressed product. Especially in the case of thermoplastic binders, it can also be necessary to subsequently cool the pressed product in the double band press with the application of area pressure.
It is known to heat the press band of the double band press at the reversing drums on the inlet side of the press so that a specific quantity of heat is transferred into the region of the so-called reaction zone, where the material to be pressed is located between the press bands and is subjected to area pressure, and to there transfer the heat to the material to be pressed. Because of the limited heat capacity of the press bands, this quantity of heat is insufficient as a rule. Heat-conducting elements have become known from DE-OS 33 25 578 with whose help additional heat can be transmitted in the reaction zone to the press bands. These heat-conducting elements consist of material with good heat-conducting properties and are arranged with one surface at the pressure plate in the double band press while assuring good heat-conducting contact. The other surface of the heat-conducting element contacts the inner sides of the press band in the region of the reaction zone in a sliding manner. The pressure plates are heated to a higher temperature than that required in the reaction zone, so that a pressure gradient is produced between the pressure plates and the press bands and the heat flow is directed from the pressure plates through the heat conducting elements to the press band. This additional heat is then transferred by the press bands to the material to be pressed or extruded. With such an arrangement, a cooling of the press bands is also possible by cooling the pressure plate.
It is known from DE-OS 24 21 296 to configure channels designed as bores in the pressure plate for heating the pressure plates in the double band press, through which channels heated fluid medium flows. A liquid, such as thermal oil or a cooling liquid or a gas or steam, is, for instance, suitable as the fluid medium. Such fluid media exchange heat with the walls of the channels. Specifically, they yield heat of the walls of the channel by means of convection in the case of a heated medium, or absorb heat from the walls of the channels by means of convection in the case of a cooled medium. These fluid media are, in the following, called heat carrier means for short. The heating of other portions of the double band press, for instance, the press stand, by a heat carrier means circulating through channels in these parts is shown in DE-OS 33 37 913.
For improving heat transmission between the heat carrier means and the pressure plate, it is further known from DE-OS 33 25 578 to configure axially extending depressions and protrusions in the walls of the channels in order to thus increase the surface of the channel inner wall. While bores with circular cross sections are comparatively easy to fabricate in the heatable or coolable parts of the double band press, such depressions and protrusions are difficult to fabricate from a production technology point of view. Furthermore, it is disadvantageous that the surface increase achieved by the protrusions and depressions is often inadequate to transfer sufficient heat between the heat carrier means and the heatable or coolable parts of the double band press.